In utilizing high power electrical systems wherein a power source, such as a high voltage generator, is connected with a load, it is often desirable to detect the existence of abnormal voltage potentials at various test points on the system components or along the electrical circuitry connecting the components. Once an abnormal voltage is detected, it is also desirable to disconnect the power source typically causing the abnormal voltage potential from the system load. Furthermore, when an abnormally high voltage potential is inadvertently produced on a system component exposed to the public or system users, the possibility of electrocution requires that the power source causing the abnormal voltage be quickly disconnected from the system.
For the purpose of crop irrigation, electrically powered sprinkler systems are often employed on farms, and particularly the large western and mid-western farms, to irrigate large areas of crops in a timely and economical manner. To irrigate the fields, water is pumped from a well and fed to the sprinkler system where it is generally uniformly distributed onto the fields by large electrically driven sprinkler arms. The sprinkler arms typically extend radially from a pivot panel and are rotationally driven by a high voltage power source such as a 480/277 volt three-phase a.c. generator.
Under normal operating conditions, the sprinkler system is normally grounded to prevent lethal voltage potentials from inadvertently developing on the exposed metallic portions of the sprinkler system. However, if the system is improperly grounded or is simply inadequately grounded, lethal voltages may be produced on the otherwise normally grounded sprinkler system. For example, if the sprinkler system is grounded by utilizing a grounding rod inserted into the ground, conductivity between the grounding rod and the ground can be greatly reduced whenever the ground is dry. The reduction in conductivity can create undesirably high voltage potentials between the sprinkler system and the ground if the sprinkler system becomes inadvertently or unintentionally charged. For example, if one of the phase conductors is inadvertently connected to the frame of the sprinkler system, lethal voltages can be produced between the ground and the exposed metallic portions of the sprinkler system, such as the frame and sprinkler arms, thereby creating obvious danger to unwary users of the sprinkler system.
In accordance with the present invention, a system is provided for electrically disconnecting the power source, such as a multi-phase a.c. generator or alternator, from a load, such as a sprinkler system, when a voltage potential in excess of a predetermined threshold is detected between a test point, such as the normally grounded metallic frame of the sprinkler system, and a selected voltage reference point, such as the ground. When used in conjunction with the manually operated systems, the threshold voltage is selected at a level generally considered to be less than lethal voltage potentials. When the system detects a voltage in excess of the threshold voltage at a selected test point, the system will automatically function to disconnect the power source from the load. When a three-phase a.c. power source is utilized with a balanced load, the system will also detect an imbalance in phase voltage in excess of the selected threshold and will disconnect the power source from the load. In a specific application, the system of the present invention will effectively detect the existence of lethal voltage potentials on normally grounded components such as a sprinkler system and will function to quickly disconnect the power source from the load to avert the possibility of the electrocution of persons contacting the normally grounded component.